Cabled core and braided suture made therefrom

ABSTRACT

A braided suture possesses a cable core which resists any tendency to protrude through the surrounding braid structure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of commonly assigned,co-pending U.S. patent application Ser. No. 07/733,362 filed Jul. 19,1991 which is a continuation of commonly assigned, now abandoned U.S.patent application Ser. No. 07/623,224 filed Dec. 5, 1990 now abandoned,which is a continuation-in-part of U.S. application Ser. No. 491,215filed Mar. 9, 1990 and now U.S. Pat. No. 5,019,093, which is acontinuation of commonly assigned, now abandoned U.S. patent applicationSer. No. 344,745 filed Apr. 28, 1989 as a continuation-in-part ofcommonly assigned, now abandoned, U.S. patent application Ser. No.227,699 filed Aug. 3, 1988 as a continuation-in-part of commonlyassigned, now abandoned, U.S. patent application Ser. No. 89,732 filedAug. 26, 1987.

BACKGROUND OF THE INVENTION

This invention relates to a braided suture of improved constructionfeaturing a cabled core component.

Sutures intended for the repair of body tissues must meet certainrequirements: they must be substantially non-toxic, capable of beingreadily sterilized, they must have good tensile strength and haveacceptable knot-tying and knot-holding characteristics and if thesutures are of the absorbable or biodegradable variety, the absorptionor biodegradation of the suture must be closely controlled.

Sutures have been constructed from a wide variety of materials includingsurgical gut, silk, cotton, a polyolefin such as polypropylene,polyamide, polyglycolic acid, polyesters such as polyethyleneterephthalate and glycolide-lactide copolymer, etc. Although the optimumstructure of a suture is that of a monofilament, since certain materialsof construction would provide a stiff monofilament suture lackingacceptable knot-tying and knot-holding properties, sutures manufacturedfrom such materials are preferably provided as braided structures Thus,for example, sutures manufactured from silk, polyamide, polyester andbioabsorbable glycolide-lactide are braided to provide optimumknot-tying and knot-holding properties.

Currently available braided suture products are acceptable in terms oftheir knot-tying and knot-holding properties. However, as removed fromthe package, they tend to be stiff and wiry and retain a "set" or"memory" such that at the time of use, it is usually necessary for thesurgeon or assistant personnel to flex and stretch the suture to make itmore readily handleable. Furthermore, the surfaces of known sutures areperceptibly rough. Thus, if one passes one's hand or fingers along thebraid, surface irregularities will be readily detected. The result ofthis rough surface is that the suture will exhibit drag or chatter as itis drawn through tissue, characteristics which militate against smooth,neat, accurately placed wound approximation so necessary to excellencein surgical practice.

By way of overcoming the foregoing disadvantages which characterizecommercially available braided sutures, U.S. Pat. No. 5,019,093describes a braided suture of improved construction possessing asignificantly greater number of sheath yarns for a given overall denier,the sheath yarns being fabricated from individual filaments of finerdenier than filaments which are typical of known types of braidedsuture, the resulting improved suture exhibiting perceptibly improvedflexibility and handling and reduced chatter and drag compared withbraided sutures of known construction.

In all but the smallest size, the sutures of U.S. Pat. No. 5,019,093 canoptionally be constructed around a filamentous core, a particularlyadvantageous feature in sutures of heavier denier In some of thesecore-containing suture constructions, the larger number of sheath yarnsin the braid may require a larger diameter core relative to that of acore of a similar braided suture constructed from fewer sheath yarns.However, a difficulty has been observed during the normal processing andhandling of sutures possessing a somewhat larger core, namely, the corehas a tendency in some cases to work through the surface sheath yarns.This "core popping" tendency can be diminished or eliminated byincreasing the braid angle (the angle at which sheath yarns cross overeach other in the braid). However, this solution to the problem of corepopping can only come at the expense of surface smoothness of the suturesince such smoothness decreases as the braid angle increases.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a braided suture possessinga cabled multifilamentous core.

It is a particular object of the invention to provide such a suturepossessing a greater number of sheath yarns, a finer denier for theindividual filaments contained in an individual sheath yarn and agreater pick count (crossovers per linear inch) for a suture of anygiven overall denier while at the same time resisting any tendency ofits core to penetrate through the outer surface of the suture.

In keeping with these and other objects of the invention, there isprovided a braided suture possessing a cabled multifilamentous corecomponent. The cabled core in accordance with the invention provides abalanced structure which remains straight and does not have a tendencyto twist upon itself or protrude through the sheath. Individual yarnsare twisted in a first direction, the "front" direction, and thenmultiple twisted yarns are twisted together in the reverse, "back",direction to form a cabled core. The cabled core should have acoefficient of twist, alpha, of at least about 24. It is alsocontemplated that multiple yarns may be plied together, i.e., alignedparallel to one another, with the plied yarns being front twisted andmultiple plied yarns being back twisted to form the cabled core of theinvention.

The term "suture" as used herein is intended to embrace bothnon-absorbable as well as the bioabsorbable varieties.

The term "braid" or "braided" as applied to the suture of this inventionrefers to an arrangement of discrete units, or bundles, denominated"sheath yarns", made up of individual filaments with individual sheathyarns interlocking or interlacing each other in a regular criss-crosspattern.

The term "cabled" as applied to the core component of the braided sutureof this invention refers to a core made up of individual yarns each ofwhich has been given a twist in one direction, the twisted yarns beingcombined to form a core which is then given a twist in a second,opposite direction.

The term "pick count" as applied to a braided suture construction refersto the number of crossovers of sheath yarns per linear inch of sutureand, together with the overall denier of the suture, the denier of theindividual filaments constituting a sheath yarn and the number of sheathyarns employed, defines the principal construction characteristics of abraided suture.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a preferred embodiment, the braided suture of the present inventionis fabricated from a bioabsorbable or biodegradable resin such as onederived from polyglycolic acid, glycolide, lactic acid, lactide,dioxanone, trimethylene carbonate, etc., and various combinations ofthese and related monomers. Sutures prepared from resins of this typeare known in the art, e.g., as disclosed in U.S. Pat. Nos. 2,668,162;2,703,316; 2,758,987; 3,225,766; 3,297,033; 3,422,181; 3,531,561;3,565,077; 3,565,869; 3,620,218; 3,626,948; 3,636,956; 3,736,646;3,772,420; 3,773,919; 3,792,010; 3,797,499; 3,839,297; 3,867,190;3,878,284; 3,982,543; 4,047,533; 4,060,089; 4,137,921; 4,157,437;4,234,775; 4,237,920; 4,300,565; and, 4,523,591; U.K. Patent No.779,291; D. K. Gilding et al., "Biodegradable polymers for use insurgery--polyglycolic/poly(lactic acid) homo and co-polymers: 1,Polymer, Volume 20, pages 1459-1464 (1979), and D. F. Williams (ed.),Biocompatibility of Clinical Implant Materials, Vol. II, ch. 9:"Biodegradable Polymers" (1981).

Although the advantages of a cabled core in accordance with thisinvention, in particular, the resistance to "core popping" mentionedabove, are conferred upon braided sutures generally which have beenconstructed with such a core, they are most fully realized in a braidedsuture constructed in accordance with the principles established in U.S.Pat. No. 5,019,093 referred to above. The defining characteristics ofthe braided suture of U.S. Pat. No. 5,019,093, apart from the materialof its construction, are:

(1) overall suture denier;

(2) the pattern of the interlocking yarns expressed in pick count, whichis to say, the number of crossovers of individual sheath yarns perlinear inch of suture;

(3) the number of sheath yarns comprising the braid;

(4) the denier of the individual filaments comprising each sheath yarn;and,

(5) the denier of the core.

(1) Overall Denier of the Suture

The overall denier of the preferred braided suture can vary from about125 to about 4000. Within this range, the ranges of overall denier forparticular sutures are: from above about 125 to about 200 denier; fromabove about 200 to about 300 denier; from above about 300 to about 500denier; from above about 500 to about 800 denier; from above about 800to about 1200 denier; from above about 1200 to about 2000 denier; and,from above about 2000 to about 4000 denier.

(2) Pattern of the Interlocking Sheath Yarns (Pick Count)

For a preferred suture of any range of overall denier, pick count canvary from about 50 to about 100 crossovers/inch with about 55-80crossovers/inch being preferred. For preferred sutures constructedwithin any range of overall denier, as larger numbers of sheath yarnsare employed, the pick-count for acceptable sutures will also increasewithin the above ranges. For a preferred suture of a particular range ofdenier and number of sheath yarns, pick count is advantageouslyestablished to achieve a balance in the properties desired. Forpreferred sutures of any specific denier range and number of sheathyarns, it is preferable to have as low a pick count as possible in orderto achieve optimum surface smoothness.

(3) The Number of Sheath Yarns

In the preferred suture, the number of sheath yarns bears some relationto overall suture denier, the number generally increasing with theweight of the suture. Thus, across the range of suture weight (denier)indicated above, the preferred braided suture can be constructed withfrom about 4 up to as many as about 36 individual sheath yarnsconstructed from individual filaments having the deniers discussedbelow.

Table I below sets forth broad and preferred ranges for the numbers ofsheath yarns which are suitable for the construction of preferredbraided sutures of various ranges of overall denier. The pick counts ofthe preferred sutures vary from about 50 to about 100 and deniers ofindividual filaments vary from about 0.2 to about 6.0 for the broadrange of number of sheath yarns and the pick counts vary from about 55to about 80 and the deniers of individual filaments vary from about 0.8to 3.0, and advantageously from about 1.0 to about 1.8, for thepreferred range of number of sheath yarns:

                  TABLE I                                                         ______________________________________                                        Number of Sheath Yarns Related to Suture Denier                                                  Number of   Number of                                      Overall Suture                                                                           Suture  Sheath Yarns                                                                              Sheath Yarns                                   Denier     Size    (Broad Range)                                                                             (Preferred Range)                              ______________________________________                                        greater than about                                                                       6/0      4-16        6-14                                          125 to about 200                                                              greater than about                                                                       5/0      4-16        6-14                                          200 to about 300                                                              greater than about                                                                       4/0     10-20       12-14                                          300 to about 500                                                              greater than about                                                                       3/0     14-20       14-18                                          500 to about 800                                                              greater than about                                                                       2/0     16-32       20-30                                          800 to about 1200                                                             greater than about                                                                       0       20-36       24-32                                          1200 to about 2000                                                            greater than about                                                                       1,2     20-36       24-32                                          2000 to about 4000                                                            ______________________________________                                    

While the sheath yarns need not be twisted, it is generally preferredthat they be provided with a twist so as to minimize snagging duringbraid construction. Alternatively, the sheath yarns can be airentangled.

(4) Individual Filament Denier

In the preferred sutures, the individual filaments comprising eachsheath yarn can vary in weight. For smaller sutures, i.e. sutures havingan overall suture denier of less than about 300, the individual sheathfilaments can vary in weight from about 0.2 to about 3.0 denier,preferably from about 1.0 to about 1.8 denier. For larger sutures, i.e.sutures having an overall suture denier of greater than about 300,individual sheath filaments can vary in weight from about 0.2 to about6.0 denier, preferably from about 0.8 to about 3.0 denier and morepreferably from about 1.0 to about 1.8 denier. The number of suchfilaments present in a particular sheath yarn will depend on the overalldenier of the suture as well as the number of sheath yarns utilized inthe construction of the suture. Table II sets forth some typical numbersof filaments per sheath yarn for both the broad and preferred ranges offilament weight:

                  TABLE II                                                        ______________________________________                                        Number of Filaments per Sheath Yarn                                           Approximate    Approximate                                                                              Filament                                            Minimum        Maximum    Denier                                              ______________________________________                                        45             450        0.2                                                 15             150        0.5                                                 5              50         1.5                                                 3              40         1.8                                                 1              15         6.0                                                 ______________________________________                                    

The individual filaments of the braided suture may be fabricated from abioabsorbable polymer derived at least in part from one or more monomersselected from the group consisting of glycolic acid, glycolide, lacticacid, and lactide. Alternatively, the individual filaments may befabricated from a non-absorbable material, e.g., cotton, silk, polyamideor polyolefin.

(5) Cabled Core

Whether or not provided as a component of the preferred type of braidedsuture construction described above or some other type of braided sutureconstruction, the cabled core component of the braided suture herein ismanufactured in a separate operation and is assembled from a pluralityof individual yarns, e.g., from about 2 to about 1500, and preferablyfrom 3 to about 1323 yarns. Each yarn comprising the core is given atwist in one direction, the "front" direction, the twisted yarns thenbeing combined into a core which is then twisted in the oppositedirection, the "back" direction, to provide the cabled core unit aroundwhich the remainder of the suture is constructed. Depending upon thematerial used to construct the core, it may be desirable to heat setand/or stretch the core in a known manner prior to final assembly of abraided suture incorporating the cabled core.

The denier of the individual yarns comprising the core is notparticularly critical and can range in most cases from about 10 to about100 and preferably from about 20 to 70. The degree of twist which isapplied to the individual yarns can vary widely with from about 200 toabout 1500 turns per meter, and preferably, from about 240 to about 1200turns per meter, generally providing good results.

The overall denier of the cabled core is, of course, determined by thenumber and individual deniers of the core yarns from which the core isconstructed. For many suture constructions, core denier will range fromabout 20 to about 80 and preferably from about 25 to about 50 in thesmallest size suture and from about 800 to about 2400 and preferablyfrom about 1000 to about 2200 in the largest size suture. In order toincrease the total core denier, it is contemplated that for largersuture cores it may be desirable to ply two or more yarns together,preferably before front twisting of the yarns.

The degree of reverse-direction or "back" twist should be determined fora particular suture construction so as to provide a balanced structure.Yarn-to-yarn twist levels can be compared through the "coefficient oftwist function" alpha which is related to the helical angle. Thecoefficient of twist function can be calculated from the relationship##EQU1## in which alpha is the coefficient of twist, K is the twistlevel in turns per meter and D is the denier of the resulting twistedproduct, e.g., twisted yarn or core. In other words, the coefficient oftwist, alpha, is given by the product of yarn twist, K, and the squareroot of yarn count, i.e. mass per unit length or linear density. Thiscoefficient of twist is also directly proportional to the helical ortwist angle in yarns having the same solid density (or melt density), soalpha determined for one material can be applied to materials of thesame density. Therefore, yarns having different deniers and the samecoefficient of twist are geometrically similar, with the coefficient oftwist thus being independent of the yarn denier.

The coefficient of twist in the cabled core construction is preferablyat least about 24, more preferably at least about 28 and most preferablyat least about 32.

To apply equal deformation to yarns of different denier, the coefficientof twist of the yarns should be the same. Yarns with higher deformationwill have a higher coefficient of twist. For many braided sutureconstructions, the twist level in turns per meter of the cabled corecomponent can range from about 200 to about 1500 turns per meter andpreferably from about 240 to about 1200 turns per meter.

More specifically, the cabled core is constructed from a plurality ofindividual yarns possessing a first twist of from about 100 to about1500 turns per meter, the twisted yarns being assembled into a corepossessing a second, opposite twist of from about 100 to about 1200turns per meter. Preferably, the individual yarns possess a first twistof from about 200 to about 1200 turns per meter, with the secondopposite twist of the core being about 200 to about 1100 turns permeter.

In practice, once the desired overall core denier and denier of theyarns used to make the core are known, the coefficient of twist may becalculated for the overall core and individual yarns in order toapproximate a balanced core structure. Equation (1) is first used todetermine the degree of back twist, K, required to obtain a core of thedesired overall core denier having a desired coefficient of twist,alpha, greater than 24. Using the same value for the coefficient oftwist, equation (1) is then solved using the denier of the individualyarns to determine the approximate degree of front twist which must beapplied to the individual yarns in order to obtain a balanced structure.

If multiple plied yarns are to be back-twisted to form the cabled core,the plied yarns are front twisted using equation (1) to determine thedegree of twist required to obtain a balanced structure. After thecabled core is constructed, a simple loop test can be performed todetermine whether a balanced structure has been achieved. In a commontest used by applicants, a one meter length of core is sampled and theends of the core sample are brought together with the remainder of thecore allowed to hang and form a loop. If the loop remains substantiallyopen, i.e., without twisting or with a twist less than 360°, the corestructure is considered balanced. However, if the loop twists more than360° (2 turns) in either direction, the structure is unbalanced andshould be modified accordingly. It should be noted that if a cabled corehas too much twist in one direction, then the loop will take a twist inthe opposite direction. Thus, if the loop twists in a back direction(z), the amount of twist applied to the core or yarn in that backdirection (z) should be increased, or the degree of twist in theopposite front direction(s) should be decreased. As will be appreciated,minor variations may be required in order to obtain the desired balancedcore structure.

For the preferred suture constructions of U.S. Pat. No. 5,019,093,applicants have found that suture size 7/0 and smaller can be madewithout a core component, and that a core optionally can be included insutures of size 6/0. Applicants have further found that cores for suturesizes 4/0, 5/0 and 6/0 can be constructed by twisting individual yarnsin the front direction and then reverse-twisting individual yarnstogether to form the cabled core of the invention. For sutures of size3/0 and larger, it is preferred to obtain the desired overall coredenier by plying multiple yarns together, then front twisting and thenback twisting the multiple plied yarns together to form the cabled core.In describing the cabled core, it is useful to identify the number offilaments in the structure in terms of the number of filaments in eachyarn times the number of yarns plied together times the number of pliedyarns which are back twisted together to form the cabled core. Thisterminology for the number of filaments in the core can be summarized informula (2) as follows: ##STR1## It will be understood that in theforegoing example, three sets of plied yarns are back twisted to formthe core, with each front twisted plied yarn consisting of seven 60filament yarns.

The following tables and examples set forth describe core and sutureconstructions suitable for making sutures in accordance with U.S. Pat.No. 5,019,093. It will be understood that the core construction may bevaried within the scope of the invention for use in constructing suturesoutside the scope of the foregoing patent.

Table III below provides some typical core deniers for sutures ofvarious deniers:

                  TABLE III                                                       ______________________________________                                        Core Denier Related to Suture Denier                                                             Denier of   Denier of                                      Overall Suture                                                                           Suture  Cabled Core Cabled Core                                    Denier     Size    (Broad Range)                                                                             (Preferred Range)                              ______________________________________                                        greater than about                                                                       6/0     20-80       25-50                                          125 to about 200                                                              greater than about                                                                       5/0     30-100      50-80                                          200 to about 300                                                              greater than about                                                                       4/0     80-150       80-120                                        300 to about 500                                                              greater than about                                                                       3/0     150-300     180-280                                        500 to about 800                                                              greater than about                                                                       2/0     250-700     350-650                                        800 to about 1200                                                             greater than about                                                                       0       400-1200     500-1000                                      1200 to about 2000                                                            greater than about                                                                       1,2     800-2400    1000-2200                                      2000 to about 4000                                                            ______________________________________                                    

Based on the foregoing, for a given preferred suture construction of aparticular overall suture denier, the range of pick count, number ofsheath yarns, denier of individual filaments and denier of the cabledcore are related to each other as follows:

                                      TABLE IV                                    __________________________________________________________________________    Braided Suture Construction Parameters                                        Overall         Number of                                                                             Denier of                                                                              Denier of                                    Suture  Pick    Sheath  Individual                                                                             Cabled                                       Denier  Count   Yarns   Filaments                                                                              Core                                         __________________________________________________________________________    greater than                                                                          from about 50                                                                         from about 4                                                                          from about 0.2                                                                         20-80                                        about 125 to                                                                          to about 100                                                                          to about 16                                                                           to about 1.8                                          about 200                                                                     greater than                                                                          from about 50                                                                         from about 4                                                                          from about 0.2                                                                         30-100                                       about 200 to                                                                          to about 100                                                                          to about 16                                                                           to about 1.8                                          about 300                                                                     greater than                                                                          from about 50                                                                         from about 10                                                                         from about 0.2                                                                         80-150                                       about 300 to                                                                          to about 100                                                                          to about 20                                                                           to about 6.0                                          about 500                                                                     greater than                                                                          from about 50                                                                         from about 14                                                                         from about 0.2                                                                         150-300                                      about 500 to                                                                          to about 100                                                                          to about 20                                                                           to about 6.0                                          about 800                                                                     greater than                                                                          from about 50                                                                         from about 16                                                                         from about 0.2                                                                         250-700                                      about 800 to                                                                          to about 100                                                                          to about 32                                                                           to about 6.0                                          about 1200                                                                    greater than                                                                          from about 50                                                                         from about 20                                                                         from about 0.2                                                                         400-1200                                     about 1200 to                                                                         to about 100                                                                          to about 36                                                                           to about 6.0                                          about 2000                                                                    greater than                                                                          from about 50                                                                         from about 20                                                                         from about 0.2                                                                         800-2400                                     about 2000 to                                                                         to about 100                                                                          to about 36                                                                           to about 6.0                                          about 4000                                                                    __________________________________________________________________________

In yet a more preferred braided suture construction, the relationship ofthe structural elements of the suture for a given suture size is setforth in Table V as follows:

                                      TABLE V                                     __________________________________________________________________________    More Preferred Braided Suture Construction Parameters                         Overall         Number of                                                                             Denier of                                                                              Denier of                                    Suture  Pick    Sheath  Individual                                                                             Cabled                                       Denier  Count   Yarns   Filaments                                                                              Core                                         __________________________________________________________________________    greater than                                                                          from about 55                                                                         from about 6                                                                          from about 0.8                                                                         25-50                                        about 125 to                                                                          to about 80                                                                           to about 14                                                                           to about 1.8                                          about 200                                                                     greater than                                                                          from about 55                                                                         from about 6                                                                          from about 0.8                                                                         50-80                                        about 200 to                                                                          to about 80                                                                           to about 14                                                                           to about 1.8                                          about 300                                                                     greater than                                                                          from about 55                                                                         from about 12                                                                         from about 0.8                                                                          80-120                                      about 300 to                                                                          to about 80                                                                           to about 14                                                                           to about 3.0                                          about 500                                                                     greater than                                                                          from about 55                                                                         from about 14                                                                         from about 0.8                                                                         180-280                                      about 500 to                                                                          to about 80                                                                           to about 18                                                                           to about 3.0                                          about 800                                                                     greater than                                                                          from about 55                                                                         from about 20                                                                         from about 0.8                                                                         350-650                                      about 800 to                                                                          to about 80                                                                           to about 30                                                                           to about 3.0                                          about 1200                                                                    greater than                                                                          from about 55                                                                         from about 24                                                                         from about 0.8                                                                          500-1000                                    about 1200 to                                                                         to about 80                                                                           to about 32                                                                           to about 3.0                                          about 2000                                                                    greater than                                                                          from about 55                                                                         from about 24                                                                         from about 0.8                                                                         1000-2200                                    about 2000 to                                                                         to about 80                                                                           to about 32                                                                           to about 3.0                                          about 4000                                                                    __________________________________________________________________________

For larger sutures, i.e. sutures having an overall suture denier greaterthan about 300, the range of pick count, number of sheath yarns, denierof individual filaments and denier of the cabled core are related toeach other as follows:

                                      TABLE VI                                    __________________________________________________________________________    Braided Suture Construction Parameters                                        Overall         Number of                                                                             Denier of                                                                              Denier of                                    Suture  Pick    Sheath  Individual                                                                             Cabled                                       Denier  Count   Yarns   Filaments                                                                              Core                                         __________________________________________________________________________    greater than                                                                          from about 50                                                                         from about 10                                                                         from about 0.2                                                                         80-150                                       about 300 to                                                                          to about 100                                                                          to about 20                                                                           to about 6.0                                          about 500                                                                     greater than                                                                          from about 50                                                                         from about 14                                                                         from about 0.2                                                                         150-300                                      about 500 to                                                                          to about 100                                                                          to about 20                                                                           to about 6.0                                          about 800                                                                     greater than                                                                          from about 50                                                                         from about 16                                                                         from about 0.2                                                                         250-700                                      about 800 to                                                                          to about 100                                                                          to about 32                                                                           to about 6.0                                          about 1200                                                                    greater than                                                                          from about 50                                                                         from about 20                                                                         from about 0.2                                                                         400-1200                                     about 1200 to                                                                         to about 100                                                                          to about 36                                                                           to about 6.0                                          about 2000                                                                    greater than                                                                          from about 50                                                                         from about 20                                                                         from about 0.2                                                                         800-2400                                     about 2000 to                                                                         to about 100                                                                          to about 36                                                                           to about 6.0                                          about 4000                                                                    __________________________________________________________________________

In a more preferred braided suture construction of larger overalldenier, the relationship of the structural elements of the suture for agiven suture size is set forth in Table VII as follows:

                                      TABLE VII                                   __________________________________________________________________________    More Preferred Braided Suture Construction Parameters                         Overall         Number of                                                                             Denier of                                                                              Denier of                                    Suture  Pick    Sheath  Individual                                                                             Cabled                                       Denier  Count   Yarns   Filaments                                                                              Core                                         __________________________________________________________________________    greater than                                                                          from about 55                                                                         from about 12                                                                         from about 0.8                                                                         80-120                                       about 300 to                                                                          to about 80                                                                           to about 14                                                                           to about 3.0                                          about 500                                                                     greater than                                                                          from about 55                                                                         from about 14                                                                         from about 0.8                                                                         180-280                                      about 500 to                                                                          to about 80                                                                           to about 18                                                                           to about 3.0                                          about 800                                                                     greater than                                                                          from about 55                                                                         from about 20                                                                         from about 0.8                                                                         350-650                                      about 800 to                                                                          to about 80                                                                           to about 30                                                                           to about 3.0                                          about 1200                                                                    greater than                                                                          from about 55                                                                         from about 24                                                                         from about 0.8                                                                         500-1000                                     about 1200 to                                                                         to about 80                                                                           to about 32                                                                           to about 3.0                                          about 2000                                                                    greater than                                                                          from about 55                                                                         from about 24                                                                         from about 0.8                                                                         1000-2200                                    about 2000 to                                                                         to about 80                                                                           to about 32                                                                           to about 3.0                                          about 4000                                                                    __________________________________________________________________________

As a result of their possessing a greater pick count and/or a greaternumber of sheath yarns for a suture of given overall denier and in somecases, a finer denier for the individual filaments making up a sheathyarn, the braided sutures of Tables IV-VII exhibit far fewer surfacediscontinuities, thereby providing sutures which are considerablysmoother than braided sutures of known construction.

It can be advantageous to apply one or more coating compositions to thebraided suture of this invention to improve such properties as surfacelubricity, knot tie-down behavior, and so forth. A variety of suturecoating compositions proposed for either or both purposes is known inthe art, e.g., those disclosed in U.S. Pat. No. 4,047,533.

It is also within the scope of this invention to impregnate the suturewith, or otherwise apply thereto, one or more medico-surgically usefulsubstances, e.g., those which accelerate or beneficially modify thehealing process when the suture is applied to a wound or surgical site.So, for example, the braided suture herein can be provided with atherapeutic agent which will be deposited at the sutured site. Thetherapeutic agent can be chosen for its antimicrobial properties,capability for promoting wound repair and/or tissue growth or forspecific indications such as thrombosis. Antimicrobial agents such asbroad spectrum antibiotics (gentamycin sulphate, erythromycin orderivatized glycopeptides) which are slowly released into the tissue canbe applied in this manner to aid in combating clinical and sub-clinicalinfections in a surgical or trauma wound site. To promote wound repairand/or tissue growth, one or several growth promoting factors can beintroduced into the suture, e.g., human growth factors such asfibroblast growth factor, bone growth factor, epidermal growth factor,platelet-derived growth factor, macrophage-derived growth factor,alveolar-derived growth factor, monocyte-derived growth factor,magainin, carrier proteins, and so forth. Some therapeutic indicationsare: glycerol with tissue or kidney plasminogen activator to causethrombosis, superoxide dismutase to scavenge tissue damaging freeradicals, tumor necrosis factor for cancer therapy or colony stimulatingfactor and interferon, interleukin-2 or other lymphokine to enhance theimmune system.

The following examples are illustrative of the braided suture of theinvention. In all cases, the suture filaments were constructed from a90-10 weight percent glycolide-L-lactide copolymer.

EXAMPLES 1-4

The cabled cores of Examples 1-4 were constructed in accordance with theparameters set forth in Table VIII as follows:

                                      TABLE VIII                                  __________________________________________________________________________    Cabled Core Construction Characteristics                                                             First Twist                                                                           Second Twist                                        No. of                                                                              Denier of                                                                           No. Of                                                                              In Turns Per                                                                          In Turns Per                                        Filaments                                                                           Individual                                                                          Yarns Meter (applied                                                                        Meter (applied                                                                        Coefficient                                                                         Cabled                                In The                                                                              Yarns In                                                                            In Each                                                                             to the  to form of    Core                             Example                                                                            Core  The Core                                                                            Plied Yarn                                                                          plied yarn)                                                                           the core)                                                                             Twist Denier                           __________________________________________________________________________    .sup. 1.sup.a                                                                      60 × 7 × 3                                                              72    7     305     250     32    1512                             2    35 × 7 × 3                                                              42    7     534     409     40     882                             3    22 × 7 × 3                                                              26    7     583     447     35     554                             4    28 × 3 × 3                                                              33    3     823     630     37     297                             __________________________________________________________________________     .sup.a see formula (2) supra                                             

Braided sutures were constructed around the cabled cores of Examples 1-4in accordance with the parameters set forth in Table IX as follows:

                                      TABLE IX                                    __________________________________________________________________________    Braided Suture Construction Characteristics                                                           Denier of                                                        Overall  No. of                                                                            Individual                                            Core of    Suture                                                                             Pick                                                                              Sheath                                                                            Yarns                                                 Example                                                                            Suture Size                                                                         Denier                                                                             Count                                                                             Yarns                                                                             Sheath                                                                            Core                                                                             % of Core                                                                           Braid Angle                              __________________________________________________________________________    1    1     2280 74  32  24  70 66    15.3                                     2    1/0   1550 80  28  24  40 57    17.4                                     3    2/0   1130 72  24  24  24 49    15.4                                     4    3/0    650 58  16  24  30 41    13.7                                     __________________________________________________________________________

In no case did core popping occur with any of the foregoing sutures thusdemonstrating the effectiveness of the cabled core in restraining anytendency of the core to penetrate the external sheath during handling ofthe suture.

EXAMPLES 5-11

The cabled cores of Examples 5-11 were constructed in accordance withthe parameters set forth in Table X as follows:

                                      TABLE X                                     __________________________________________________________________________    Cabled Core Construction Characteristics                                                                Front Twist                                                                   In Turns                                                                             Back Twist                                        No. of                                                                              Denier of                                                                           Denier   Per Meter                                                                            In Turns                                          Filaments                                                                           Individual                                                                          Of Each                                                                            Total                                                                             Applied                                                                              Per Meter                                                                           Coefficient                                 In The                                                                              Yarns In                                                                            Plied                                                                              Core                                                                              To Each                                                                              To Form                                                                             Of Back                                Example                                                                            Core  Core  Yarn Denier                                                                            Plied Yarn.sup.b                                                                     Cable Core                                                                          Twist                                  __________________________________________________________________________    5    69 × 7 × 3                                                              110   770  2,310                                                                             250    278   44.5                                   6    48 × 7 × 3                                                              77    540  1,617                                                                             320    324   43.5                                   7    27 × 7 × 3                                                              43    300  900 590    505   50.5                                   8    17 × 7 × 3                                                              27    190  570 640    576   45.8                                   9    54 × 1 × 3                                                              86     86  258 830    854   45.7                                   10   23 × 1 × 3                                                              37     37  110 1,000  1,035 36.3                                   11   17 × 1 × 3                                                              27     27  80  1,200  1,200 36.0                                   __________________________________________________________________________     .sup.b In Examples 9, 10 and 11, only unplied yarn was used              

Braided sutures were constructed around the cabled cores of Examples5-11 in accordance with the parameters set forth in Table XI as follows:

                                      TABLE XI                                    __________________________________________________________________________    Braided Suture Construction Characteristics                                                   Pick                                                                     Overall                                                                            Count                                                                              No. of                                                   Core of    Suture                                                                             Picks                                                                              Sheath                                                                            Denier of                                                                             % of                                         Example                                                                            Suture Size                                                                         Denier                                                                             Per Inch                                                                           Yarns                                                                             Sheath                                                                            Core                                                                              Core                                                                             Braid Angle                               __________________________________________________________________________    5    2     3,190                                                                              79   32  870 2,320                                                                             73 18                                        6    1     2,380                                                                              79   32  770 1,610                                                                             68 18                                        7    0     1,580                                                                              83   28  670 910 58 17                                        8    2/0   1,150                                                                              88   24  580 570 50 17                                        9    3/0     690                                                                              63   16  430 260 38 16                                        10   4/0     440                                                                              79   12  330 110 25 16                                        11   5/0     300                                                                              55    8  220  80 27 15                                        __________________________________________________________________________

COMPARATIVE EXAMPLES 12-16

The cabled cores of Comparative Examples 12-16 were constructed inaccordance with the parameters set forth in Table XII as follows:

                                      TABLE XII                                   __________________________________________________________________________    Cabled Core Construction Parameters                                                                   First Twist                                                                           Second Twist                                       No. of             In Turns Per                                                                          In Turns                                      Compar-                                                                            Filaments                                                                            Denier of                                                                           No. Of                                                                              Meter (applied                                                                        Per Meter                                                                            Coefficient                                                                         Cabled                           ative                                                                              In The Yarns In                                                                            Yarns In                                                                            to each applied to                                                                           of    Core                             Example                                                                            Core   Each Ply.sup.c                                                                      Each Ply.sup.c                                                                      plied yarn).sup.c                                                                     the core)                                                                            Twist Denier                           __________________________________________________________________________    12   110 × 3 × 3                                                              132   3     193     120    14    1188                             13   60 × 3 × 3                                                               70    3     438     257    22    648                              14   50 × 3 × 3                                                               60    3     193      85     7    540                              15   50 × 3 × 3                                                               60    3     193      85     7    540                              16   60 × 1 × 3                                                               70    1     560     430    21    216                              __________________________________________________________________________     .sup.c In Comparative Example 16, only unplied yarn was used             

Braided sutures were constructed around the cores of ComparativeExamples 12-16 in accordance with the parameters set forth in Table XIIIas follows:

                                      TABLE XIII                                  __________________________________________________________________________    Braided Suture Construction Characteristics                                   Core of                 Denier of                                             Compar-    Overall  No. of                                                                            Individual                                            ative      Suture                                                                             Pick                                                                              Sheath                                                                            Yarns                                                 Example                                                                            Suture Size                                                                         Denier                                                                             Count                                                                             Yarns                                                                             Sheath                                                                            Core                                                                             % of Core                                                                           Braid Angle                              __________________________________________________________________________    12   1     1960 79  32  24  132                                                                              60    15.7                                     13   1/0   1320 74  28  24  72 49    15.6                                     14   2/0   1120 86  24  24  60 48    20.0                                     15   2/0   1120 78  24  24  60 48    17.5                                     16   3/0    600 80  16  24  72 36    14.8                                     __________________________________________________________________________

In every case core popping was observed. This appears to have been dueto low coefficient of twist (below 24).

What is claimed is:
 1. A braided suture comprising a cabled coresurrounded by a sheath, wherein for a given range of overall suturedenier, the range of pick count, number of sheath yarns, denier ofindividual filaments contained in a sheath yarn and denier of the cabledcore are related to each other as follows:

    ______________________________________                                                                            Denier                                    Overall           Number of Denier of                                                                             of                                        Suture  Pick      Sheath    Individual                                                                            Cabled                                    Denier  Count     Yarns     Filaments                                                                             Core                                      ______________________________________                                        greater from about                                                                              from about                                                                              from about                                                                             20-80                                    than about                                                                            50 to     4 to      0.2 to                                            125 to  about 100 about 16  about 1.8                                         about 200                                                                     greater from about                                                                              from about                                                                              from about                                                                             30-100                                   than about                                                                            50 to     4 to      0.2 to                                            200 to  about 100 about 16  about 1.8                                         about 300                                                                     greater from about                                                                              from about                                                                              from about                                                                             80-150                                   than about                                                                            50 to     10 to     0.2 to                                            300 to  about 100 about 20  about 6.0                                         about 500                                                                     greater from about                                                                              from about                                                                              from about                                                                            150-300                                   than about                                                                            50 to     14 to     0.2 to                                            500 to  about 100 about 20  about 6.0                                         about 800                                                                     greater from about                                                                              from about                                                                              from about                                                                            250-700                                   than about                                                                            50 to     16 to     0.2 to                                            800 to  about 100 about 32  about 6.0                                         about 1200                                                                    greater from about                                                                              from about                                                                              from about                                                                            400-1200                                  than about                                                                            50 to     20 to     0.2 to                                            1200 to about 100 about 36  about 6.0                                         about 2000                                                                    greater from about                                                                              from about                                                                              from about                                                                            800-2400                                  than about                                                                            50 to     20 to     0.2 to                                            2000 to about 100 about 36  about 6.0                                         about 4000                                                                    ______________________________________                                    


2. The braided suture of claim 1, wherein for a given overall suturedenier, the range of pick count, number of sheath yarns, denier ofindividual filaments comprising a sheath yarn and denier of the cabledcore are related to each other as follows:

    __________________________________________________________________________    Overall         Number of                                                                             Denier of                                                                              Denier of                                    Suture  Pick    Sheath  Individual                                                                             Cabled                                       Denier  Count   Yarns   Filaments                                                                              Core                                         __________________________________________________________________________    greater than                                                                          from about 55                                                                         from about 6                                                                          from about 0.8                                                                         25-50                                        about 125 to                                                                          to about 80                                                                           to about 14                                                                           to about 1.8                                          about 200                                                                     greater than                                                                          from about 55                                                                         from about 6                                                                          from about 0.8                                                                         50-80                                        about 200 to                                                                          to about 80                                                                           to about 14                                                                           to about 1.8                                          about 300                                                                     greater than                                                                          from about 55                                                                         from about 12                                                                         from about 0.8                                                                          80-120                                      about 300 to                                                                          to about 80                                                                           to about 14                                                                           to about 3.0                                          about 500                                                                     greater than                                                                          from about 55                                                                         from about 14                                                                         from about 0.8                                                                         180-280                                      about 500 to                                                                          to about 80                                                                           to about 18                                                                           to about 3.0                                          about 800                                                                     greater than                                                                          from about 55                                                                         from about 20                                                                         from about 0.8                                                                         350-650                                      about 800 to                                                                          to about 80                                                                           to about 30                                                                           to about 3.0                                          about 1200                                                                    greater than                                                                          from about 55                                                                         from about 24                                                                         from about 0.8                                                                          500-1000                                    about 1200 to                                                                         to about 80                                                                           to about 32                                                                           to about 3.0                                          about 2000                                                                    __________________________________________________________________________


3. The braided suture of claim 2, wherein the cabled core is constructedwith a coefficient of twist at least about
 24. 4. The braided suture ofclaim 3, wherein the coefficient of twist is at least about
 28. 5. Thebraided suture of claim 4, wherein the coefficient of twist is at leastabout
 32. 6. The braided suture of claim 1, wherein the individualfilaments are fabricated from a non-absorbable material.
 7. The braidedsuture of claim 6 wherein the non-absorbable material is cotton, silk,polyamide or polyolefin.
 8. The braided suture of claim 1 wherein theindividual filaments are fabricated from a bioabsorbable polymer.
 9. Thebraided suture of claim 8 wherein the individual filaments arefabricated from a polymer derived at least in part from one or moremonomers selected from the group consisting of glycolic acid, glycolide,lactic acid and lactide.
 10. The braided suture of claim 1 wherein thecabled core is constructed from a plurality of individual yarnspossessing a first twist of from about 100 to about 1500 turns permeter, the twisted yarns being assembled into a core possessing asecond, opposite twist of from about 100 to about 1200 turns per meter.11. The braided suture of claim 1 wherein the cabled core is constructedfrom a plurality of individual yarns possessing a first twist of fromabout 200 to about 1200 turns per meter, the twisted yarns beingassembled into a core possessing a second, opposite twist of from about200 to about 1100 turns per meter.
 12. The braided suture of claim 1surface coated with a composition enhancing one or more functionalproperties of the suture.
 13. The braided suture of claim 1 containingat least one medico-surgically useful substance.
 14. A braided suturecomprising a cabled core surrounded by a sheath wherein for a givenrange of overall suture denier, the range of pick count, number ofsheath yarns, denier of individual filaments comprising a sheath yarnand denier of the cabled core are related to each other as follows:

    __________________________________________________________________________    Overall         Number of                                                                             Denier of                                                                              Denier of                                    Suture  Pick    Sheath  Individual                                                                             Cabled                                       Denier  Count   Yarns   Filaments                                                                              Core                                         __________________________________________________________________________    greater than                                                                          from about 50                                                                         from about 10                                                                         from about 0.2                                                                         80-150                                       about 300 to                                                                          to about 100                                                                          to about 20                                                                           to about 6.0                                          about 500                                                                     greater than                                                                          from about 50                                                                         from about 14                                                                         from about 0.2                                                                         150-300                                      about 500 to                                                                          to about 100                                                                          to about 20                                                                           to about 6.0                                          about 800                                                                     greater than                                                                          from about 50                                                                         from about 16                                                                         from about 0.2                                                                         250-700                                      about 800 to                                                                          to about 100                                                                          to about 32                                                                           to about 6.0                                          about 1200                                                                    greater than                                                                          from about 50                                                                         from about 20                                                                         from about 0.2                                                                         400-1200                                     about 1200 to                                                                         to about 100                                                                          to about 36                                                                           to about 6.0                                          about 2000                                                                    greater than                                                                          from about 50                                                                         from about 20                                                                         from about 0.2                                                                         800-2400                                     about 2000 to                                                                         to about 100                                                                          to about 36                                                                           to about 6.0                                          about 4000                                                                    __________________________________________________________________________


15. The braided suture of claim 14, wherein for a given range of overallsuture denier, the range of pick count, number of sheath yarns, denierof individual filaments comprising a sheath yarn and denier of thecabled core are related to each other as follows:

    __________________________________________________________________________    Overall         Number of                                                                             Denier of                                                                              Denier of                                    Suture  Pick    Sheath  Individual                                                                             Cabled                                       Denier  Count   Yarns   Filaments                                                                              Core                                         __________________________________________________________________________    greater than                                                                          from about 55                                                                         from about 12                                                                         from about 0.8                                                                          80-120                                      about 300 to                                                                          to about 100                                                                          to about 14                                                                           to about 3.0                                          about 500                                                                     greater than                                                                          from about 55                                                                         from about 14                                                                         from about 0.8                                                                         180-280                                      about 500 to                                                                          to about 80                                                                           to about 18                                                                           to about 3.0                                          about 800                                                                     greater than                                                                          from about 55                                                                         from about 20                                                                         from about 0.8                                                                         350-650                                      about 800 to                                                                          to about 80                                                                           to about 30                                                                           to about 3.0                                          about 1200                                                                    greater than                                                                          from about 55                                                                         from about 24                                                                         from about 0.8                                                                          500-1000                                    about 1200 to                                                                         to about 80                                                                           to about 32                                                                           to about 3.0                                          about 2000                                                                    greater than                                                                          from about 55                                                                         from about 24                                                                         from about 0.8                                                                         1000-2200                                    about 2000 to                                                                         to about 80                                                                           to about 32                                                                           to about 3.0                                          about 4000                                                                    __________________________________________________________________________


16. The braided suture of claim 15, wherein the cabled core isconstructed with a coefficient of twist at least about
 24. 17. Thebraided suture of claim 16, wherein the coefficient of twist is at leastabout
 28. 18. The braided suture of claim 17, wherein the coefficient oftwist is at least about
 32. 19. The braided suture of claim 14, whereinthe individual filaments are fabricated from a non-absorbable material.20. The braided suture of claim 19 wherein the non-absorbable materialis cotton, silk, polyamide or polyolefin.
 21. The braided suture ofclaim 14 wherein the individual filaments are fabricated from abioabsorbable polymer.
 22. The braided suture of claim 21 wherein theindividual filaments are fabricated from a polymer derived at least inpart from one or more monomers selected from the group consisting ofglycolic acid, glycolide, lactic acid and lactide.
 23. The braidedsuture of claim 14 wherein the cabled core is constructed from aplurality of individual yarns possessing a first twist of from about 100to about turns per meter, the twisted yarns being assembled into a corepossessing a second, opposite twist of from about 100 to about 1200turns per meter.
 24. The braided suture of claim 23 wherein the cabledcore is constructed from a plurality of individual yarns possessing afirst twist of from about 200 to about turns per meter, the twistedyarns being assembled into a core possessing a second, opposite twist offrom about 200 to about 1100 turns per meter.
 25. The braided suture ofclaim 14 surface coated with a composition enhancing one or morefunctional properties of the suture.
 26. The braided suture of claim 14containing at least one medico-surgically useful substance.